Analog systems and digital systems are commonly implemented in an integrated circuit using system on-chip (SOC) technology. Such systems commonly include an analog front end (AFE) circuit. The AFE circuit operates as an interface between an external input terminal, through which analog signals are input, and a digital signal processing unit that processes the received signals in digital format.
The AFE circuit is widely used in various devices, such as down converters for wireless digital communication devices, digital image scanners, digital cameras and voice codecs, and the like. The AFE circuit includes an amplifier and an analog to digital converter (ADC). The amplifier amplifies the received analog input signal, and the ADC converts the amplified analog input signal into digital signal. The amplifier has gain and offset errors across different gain settings. These errors introduce spurs and results in degradation in performance of the ADC.
Also, in real world applications, an analog input signal has high peak to average ratio. As a result, a dynamic range of the ADC is under-utilized. An existing solution is to use a variable gain amplifier in the analog signal chain before the ADC. The variable gain amplifier amplifies the analog input signal when the amplitude is low and keeps the analog input signal intact when the amplitude is high. This allows use of the entire dynamic range of the ADC. However, to reconstruct the signal digitally, the variable gain operation has to be performed digitally. As the gain of the variable gain amplifier is not known accurately and can change with temperature and other variations, the digital compensation can cause analog input signal distortion.